The invention relates to a filter arrangement comprising a balanced amplifier having an inverting input, a non-inverting input, an inverting output, a non-inverting output, a first input terminal and a second input terminal, a first feedback circuit comprising a first capacitor and arranged between the non-inverting output and the inverting input, and a second feedback circuit comprising a second capacitor substantially identical to the first capacitor and arranged between the inverting output and the non-inverting input.
Such a filter arrangement is known from U.S. Pat. No. 4,509,019. Said filter arrangement constitutes an integrator. Between the two input terminals and the two inputs of its amplifier two MOS resistors are arranged. The resistance values of these resistors can be adjusted by means of a control voltage applied to the gate electrode. This control voltage enables the RC-time constant of the resistor and the capacitor to be adjusted to the desired value.
A balanced input voltage is applied to the first input terminal and the second input terminal of the filter arrangement and a balanced output voltage is available on the inverting output and the non-inverting output of the amplifier. This output voltage is substantially exempt of even-order harmonic distortion, which is caused inter alia by non-linearities of the MOS resistors. This is because such distortions are cancelled as a result of the balanced drive and the symmetrical construction of the arrangement.
A drawback of this known arrangement is that the time constant of the arrangement is only adjustable over a comparatively small range, because the resistance values of the MOS transistors can be varied only over a comparatively small range.